Electrical heating element



E. L. WIEGAND ELECTRICAL HEATING ELEMENT Filed March 21, 1939.

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E I E m AT'l-o Kuajs Patented Feb. 10,1942

UNITED STATES PATENT OFFICE 2,272,282 ELEc'rRIoAL. HEATING ELEMENT Edwin L. Wiegand, Pittsburgh, Pa. Application March 21, 1939, Serial No. 263,178 (01. 201-454) I 19 Claims.

My invention relates to electrical heating elements of the type comprising a resistor disposed within and insulated from a tubular metallic sheath. The principal object of my invention is to provide new and improved electrical heating elements or said type.

In the drawing accompanying this application, I have shown, for purposes or illustration, an electrical heating element of the aforesaid type, which may assume variousiorms and may be insulated in various ways, as will appear as the'description of the invention proceeds, and in this drawing:

Figure l is a side elevation of an electrical heating element of the type in which the in yention may be embodied,

Figure 2 is a longitudinal section of a portion 7 or the heating element shown in Figure l, and

Figures 3, d, and aresections taken along the lines l-ll, and 5-5, of Figure 2, respectively, looking in the direction of the ar rows. I W

The particular heating element shown in the drawing comprises an elongated tubular metallic sheath Ell, in this instance oi circular cross-sectional'outline, in which is disposed a resistor in, here shown as a helix of resistance wire. A leadin conductor 22, here shown as comprising a leadin wire 23 and a terminal t l, is provided. One end of the lead-in wire 23 is mechanically and electrically connected to'an end of the resistor it, and the other end of the lead-1n wire is mechanically and electrically connected to the terminal 22 3. The terminal 25 is here shown as generally cylindrical, and as extending a desired distance into the open end 255 of the tubular sheath "it. The lead-in wire 23 is here shown as connected to the terminal "2 i by the provision of a central, longitudinally extending hole 25 in the terminal 2t in which hole the lead-in wire 23 is disposed, and the end of the wire 23 may be fastened to the terminal M by swaging the terminal against and about the wire as indicated, at 2'3. The free end of th terminal 24- is here shower as provided with threads.

The terminal 24 is here shown as spaced and insulated from the inside of the tubular sheath.

by an insulating'bush'mg 28. This bushing, 28, may be made of a single piece of suitable insulating material, or it may be made built-up of laminae made of some integral material, such as mica or any other suitable material. The end portion or the sheath 2B is n'ot'subjected to very high temperatures so that fact may be taken into account in the of the bushing 28. The shath 20 may be swaged :against and about the bushing 28, as indicated The other end of the iiided with a terminal heating element is pro 21a insulated from the selection of the-material It will be understood bushing 28d. Within the the sheath. The sheath desired configuration; or

'be considered as divided into a zone 0,

sheath .20 by a bushing 28a, as hereinbefore described in connection with the terminal 24 and bushing 28. The end of the resistor 2|, opposite from that shown in Figure 2, may be connected by a lead-in wire (not shown), similar to the lead-in wire 23, to the terminal 24a, as already described in connection with the lead-in wire it and the terminal 2d.

The heating element illustrated may be con- "sidered as comprising what may be termed a principal insulated zone a which extends from the inside of the bushing 2% to the inside of the sheath 2% in the zone tithe resistor 2i and lead-in wire 23 are embedded in insulating material 3B which initially may be in a comrninuted or powdered state, but which in the final condition of the heating ele ment desirably is compacted to a hard dense mass. It will be understood that the initial form or state of the insulating material 38, in which it is introduced into the sheath 20, may be var led, and varied to suit-any desired method ct" introducing it or the resistor 2i, or both, into 2t initially may be of a different form or size and may be brought to final condition by working-as by drawing and elongating, thus compressing and compacting the insulating material 3Q, on the other hand, the insulating material bill may be compacted by vibration, or in any other desired and suitable way. Also, the sheath til need not be drawn and elongated, but initially may have the same general form as when the element is completed. of course that even after the heating element is otherwise completed it may be bent so that its longitudinal axis is oi a it may have its crosssectional outline altered, as by compression, or otherwise. 1

In general, the insulating material 30, in the zone a may, if desired, have mixed therewith a binding or cementing material, as clay, or any other suitable binder.

For the purpose of considering the invention in its more specific aspects, the zone a first may which is occupied by the resistor 2|, and, as the ends of the zone c are spaced a desired and suitable distance from the ends of the sheath 20, this leaves a zone 12 between each end of the zone 0 and the respective ends of the sheath 20. The zone 0 is of course a high temperature zone andthe insulating material in at least this zone should be a suitable refractory insulating material, for examplefsilica, or silicate, ior example, zircon or any refractory oxide or combination of refractory oxide or any other suitable, refractory insulating material, desirably of and desirably having good a mineral character,

heat-conducting properties. Crystalline oxides or silicates are desirable. As will appear, such materials need not however be confined to the zone 0, although it crystalline magnesium oxide or any other unstable refractory insulating material, is utilized in the zone c, it should, in accordance with the present invention, not be used in the whol length of the zone b, as will further appear.

If the zone is occupied by an unstable oxide such as crystalline magnesium oxide, then a portion of the length of the zone b, or theentire zone b, should comprise an insulating material which will serve to entrap moisture which may enter through the bushing, or between the bushing and the sheath. Thus, if desired, the entire zone b may comprise a stable oxide, or a stable silicate, desirably crystalline. By way of example, zircon, silica, aluminum oxide, or any other stable oxide or silicate may be utilized. It will be evident that the interposition of a zone of suitable length of such stable material between unstable crystalline magnesium oxide and an end of the sheath 20 will prevent such an amount of moisture as is likely to enter the end of the sheath under ordinary conditions from reaching the unstable material. Both the unstable and stable material will thus remain unchanged and the moisture entrapped by the stable material will be driven oil by heat upon subsequent use of the heating element.

Under some conditions, by way of example, more severe conditions of use, I prefer to utilize an active sorbent material, that is, a material having active water absorbing capacity, or active water adsorbing capacity, in all of the zone I) or a portion of the zone b. Such material, desirably of granular form, will sorb relatively large amounts of moisture, and the material may be brought to its original activated state upon heating.

In case an active sorbent material is used, activated alumina, or silica gel (activated silicon oxide), or any other suitable material of like nature may be used. It is necessary in selecting such a sorbent granular material to choose a material which does not alter physically when saturated or unsaturated and which may be reactivated by heat, desirably an infinite number of times, at operating temperatures which can normally be assigned to the portion of the heating element containing this material, in fact at the lowest temperature in the heating element. Its electrical resistivity must, of course, be suitably high. Such materials as activated alumina, silica gel, and the like, may be termed reversible sorbents, and may be described as having reversible water sorbing capacity. When a reversible sorbent is utilized, and if the zone c comprises an unstable material, such as crystalline magnesium oxide, the zone I) may comprise a reversible sorbent, or the zone I) may be divided into two zones d and e, the zone 11 comprising a reversible sorbent and the zone e comprising a stable refractory oxide or silicate, examples of which have been hereinbefore given. By way of example, the zone c may comprise crystalline magnesium oxide, the zone e may comprise zircon and the zone d may comprise activated alumina. 0n the other hand, a zone comprising a reversible sorbent may be utilized even though the zone 0 comprises a stable refractory insulating material. Thus, the zone 0 may comprise a stable refractory insulating materiaL. preferably a stable crystalline oxide or silicate, and the zone I; may

comprise a reversible sorbent; or the zone 0 may comprise a stable refractory insulating material, preferably a stable crystalline oxide or silicate, and the zone e may comprise stable refractory insulating material either the same as or different from the material in the zone 0, and the zone (1 may comprise a reversible sorbent. It may be stated that even if the zone 0, as well as the zone e comprises stable insulating material it is desirable to guard against the entrance of moisture which, either by reason of long inactivity of the heating element under unfavorable atmospheric conditions, or by reason of other condi' ticns of use, may reach the material in which the resistor is embedded, and, upon connection of the heating element to a source of current, so as to at once operate it at full capacity, may result in rupture of the tubular sheath 20, or otherwise cause failure of the element. If the heating element contains an unstable refractory insulating material, protection against moisture is all the more important, since, for example, crystalline magnesium oxide will hydrate and swell in the presence of moisture and disruption of the sheath 20 may result, so that the heating element may be ruined for that reason alone, even before connection to a source of current. Some water, of course, may be driven off from hydrated magnesium oxide, in the range of tem peratures attained in the heating element, but after hydration it cannot be regenerated by temperatures in that range. Moreover, after hydration, initially crystalline magnesium oxide is no longer crystalline. Accordingly, as distinguished from a stable insulating material, or as distinguished from a material having reversible water sorbing capacity, crystalline magnesium oxide is unstable, is irreversible, and has irreversible water sorbing capacity, under the conditions hereinbefore set forth. It will, therefore, be evident that, if the zone 0 comprises unstable insulating material, access of moisture thereto is undesirable whether the material swells upon hydration, or whether it loses certain physical properties, such as its crystalline nature, for example, or is otherwise undesirably altered.

It will be apparent from the foregoing that the length of any given insulation zone is not necessarily restricted to the examples of length given on the drawing. Thus, any zone may be longer or shorter than illustrated; or may even be merged entirely with another zone or zones, depending upon whether one or more different insulating materials are utilized as hereinbefore set forth.

From the foregoing it will be apparent to those skilled in the art that each of the disclosed embodiments of my invention provides a new and improved electrical heating element, and accordin ly, each accomplishes the principal object of my invention. On the other hand, it also will be obvious to those skilled in the art that the disclosed embodiments of my invention may be variously changed and modified, or features thereof, singly or collectively, embodied in other combinations than those disclosed, without departing from the spirit of my invention, or sacrificing all oi. the advantages thereof, and that accordingly, the disclosure herein is illustrative only, and my invention is not limited thereto.

I I claim:

1. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor in a terminal zone, extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within-said sheath, in which said resistor is disposed, at least a transverse sectional portion of said terminal zone being occupied by a mass of particles of reiractorpvelectrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least a substantial amount of refractory electrical-insulatingmaterial having reversible water sorbing capacity.

2. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor some within said sheath and having an end spaced from an end of said sheath; a lead-in conductor in a terminal zone. extending into said end oi said sheath longitudinally of said sheath and connected to said end of said resis= tor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor is disposed, at least a transverse sectional portion of said terminal zone being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said herrier means comprising at least a substantial amount of activated alumina.

prising at least a substantial amount of activated alumina.

5. an electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said endof said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least 3. An electrical heating element, comprising: 7

a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of saidsheath I longitudinally of said sheath and connected to said end or" said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising refractory electrical-insulating unstable material having irreversible water sorbing capacity, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said unstable material being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, saidbarrler means comprising at least a substantial amount of refractory electrical-insulating material having reversible water sorbing capacity.

d. an electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising refractory electrical-insulating unstable material having irreversible water sorbing capacity, and at least a transverse sectional portion of ;an end zone extending from said end of said sheath to said unstable material being occupied by a mass v of particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means coma portion of said resistor zone comprising refractory electrical-insulating unstable material having irreversible water sorbing capacity, and at least a transverse sectional portion of an end.

zone extending from said end of said sheath to said unstable material being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means cormprising at least a substantial amount of refractory electrical-insulating material having reversible, water sorbing capacity, and a transverse sectional portion of said end zone intermediate said barrier means and said unstable material being occupied by refractory crystalline electrical-insulating material substantially lacking water sorbing capacity.

6. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end or said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising refractory electrical-insulating unstable material having irreversible water sorbing capacity, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said unstable material being occupied by a mass of particles of refractory electrical-insulating material' having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least a substantial amount of refractory electrical-insulating material having reversible water sorbing capacity, and a transverse sectional portion of said end zone intermediate said barrier means and said unstable material being occupied by refractory electrical-insulating Ina- -terial substantially lacking Water sorbin capacits.

7. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electricalinsulating material, disposed.v within said sheath, in which said resistor and said. lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising crystal= line magnesium oxide, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said portion comprising crystalline magnesium oxide being occupied by a mass of particles of refractory electricalinsulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least a substantial amount of refractory electrical-insulating material having reversible water sorbing capacity.

8. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising crystalline magnesium oxide, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said unstable material being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least a substantial amount of activated alumina.

9. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said shflath and having any end spaced from an end said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said reslstorand said leading conductor aredisposed, said material in at least a portion of said resistor zone comprising crystalline magnesium oxide, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said portion comprising crystalline magnesium oxide being occupied by a mass of particles of refractory electrical-insulating material constituting 'barrier means for intercepting moisture, said barriermeans comprising at least a substantial amount of refractory electrical-insulating material having reversible water sorbing capacity, and a transverse sectional portion of said end zone intermediate said barrier means and said portion comprising crystalline magnesium oxide being occupied by refractory electrical-insulating material substantially lacking water sorbing capacity.

10. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally 01' said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising crystalline magnesium oxide, and at least a transverse sectional portion of an end zone extending from said end or said sheath to said portion comprising crystalline magnesium oxide being occupied by a mass of particles or refractory electrical-insulating 'material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least'a substantial amount of activated alumina, and a transverse sectional portion of said end zone intermediate said barrier means and said portion comprising crystalline magnesium oxide being occupied by refractory electrical-insulating material ing water sorbing capacity.

11. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an'end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed said material in at least a portion of said resistor zone comprising crystalline magnesium oxide, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said portion comprising crystalline magnesium oxide being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier substantially lackmeans for intercepting moisture, said barrier means comprising at least a substantial amount of activated alumina, and a transverse sectional portion of said end zone intermediate said barrier means and said portion comprising crystallinemagnesium oxide being occupied by refractory electrical-insulating material substantially lacking water sorbing capacity and consisting mainly of zircon.

12. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor in a terminal zone, extending into said end of said sheath longitudinally of said sheath connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor is disposed, at least a transverse sectional portion oi said terminal zone being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presence 01 moisture and constituting, barrier means for intercepting moisture, said barrier means comprising at least a substantial amount of silica gel.

13. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor 7 zone Within said sheath and having an end spaced from an end of said sheath; a lead-4n conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which saidresistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising refractory electrical-insulating unstable material having irreversible water sorbing capacity, and at least a, transverse sectional portion of an end zone extending from said end of said sheath to said unstable material being occupied by a mass oi particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least a substantial amount of silica gel.

14. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an 'end spaced from an end of said sheath; a lead-in sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising refractory electrical-insulating unstable material having irreversible water sorbing capacity, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said unstable material being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least a substantial amount of refractory electrical-insulating material having reversible water sorbing capacity, and a transverse sectional portion of said end zone intermediate said barrier means and said unstable material being occupied by refractory electrical-insulating material substantially lacking water sorbing capacity and consisting mainly of zircon.

15. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory'electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising refractory electrical-insulating unstable material having irreversible water sorbing capacity, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said unstable material being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for' intercepting moisture, said barrier means comprising at least a substantial amount of activated alumina, and a transverse sectional portion of said end zone intermediate said barrier means and said unstable material being occupied by refractory electrical-insulating material substantially lacking water sorbing capacity.

16. An electrical heating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising refractory electrical-insulating unstable material having irreversible water sorbing capacity, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said unstable'material being occupied by a mass of particles of refricatory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least 'a substantial amount of silica geL'and a transverse sectional portion of said end zone intermediate saidbarrier means and said unstable material being occupied by refractory electrical-insulating material substantially lacking water sorbing capacity. 17. An electrical heating element, comprising:

a tubular metallic sheath; a resistor in a resistor zone Within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheathdongitudinally of said sheath and connected to said end of said resistor; and refractory electricalinsulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising crystalline magnesium oxide, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said unstable material being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presenc of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least ,a substantial amount of silica gel.

18. An electrical heating element, comprising: 7

a tubular metallic sheath; aresistor in a resistor zone within said sheath .and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory electrical-insulating material, disposed within said sheath, in which said resistor and said lead-in conductor are disposed, said material in at least a portion of said resistor zone comprising crystalline magnesium oxide, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said portion comprisingcrystalline-magnesium oxide being occupied by a mass of particles of refractory electrical-insulating material having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least a substantial amount of silica gel, and a transverse sectional portion of said end zone intermediate said barrier means and said portion comprising crystalline magnesium oxide being occupied by refractory electrical-insulating material substantially lacking water sorbing capacity.

19. An electricalheating element, comprising: a tubular metallic sheath; a resistor in a resistor zone within said sheath and having an end spaced from an end of said sheath; a lead-in conductor extending into said end of said sheath longitudinally of said sheath and connected to said end of said resistor; and refractory elec-' trical-insulating material, disposed within said "sheath, in which said resistor and said lead-in conductor are disposed said material in at least aportion of said resistor zone comprising crystalline magnesium'oxide, and at least a transverse sectional portion of an end zone extending from said end of said sheath to said portion comprising crystalline magnesium oxide being occupied by a mass of particles of refractory electrical-insulating material'having desired stability in the presence of moisture and constituting barrier means for intercepting moisture, said barrier means comprising at least a substantial amount of silica gel, and a transverse sectional portion of said end zone intermediate said barrier means and said portion comprising crystalline magnesium oxide being occupied by refractory electrical-insulating material substantially lack. ing water sorbing capacity and consisting mainly of zircon.

- EDWIN L. WIEGAND. 

